Public Access
twislaandClaude Opus 5.5
468dc0dc0d
For carrying on a download that broke (issue #54): the head's ETag and Content-Range are read, a 206 is checked to be the rest of the same file, and a policy says how many tries a download is worth. Host-tested. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk
54 lines
2.3 KiB
C++
54 lines
2.3 KiB
C++
#pragma once
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#include <string>
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#include "http_head.h"
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namespace roro::release {
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// Carrying on a download that broke (issue #54): the connection is opened again with
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// "Range: bytes=<from>-", and what was already received stays where it is. The Update File's own
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// hash and signature are what decide whether the whole is good; these checks only keep the device
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// from carrying on with something that plainly is not the rest of the same file.
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// The validator to send as "If-Range", so a file that changed comes back whole (a 200) instead of
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// in part: only a strong ETag may be used for that. "" for none.
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inline std::string ifRangeFor(const std::string& etag) {
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return etag.size() >= 2 && etag.front() == '"' && etag.back() == '"' ? etag : "";
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}
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// Is this answer the rest of the file, from byte `from` of `total`? "" if so, or why not, in
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// words for the screen. `etag` is what the first answer gave ("" if nothing).
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inline std::string resumeRefusal(const HttpHead& head, long from, long total, const std::string& etag) {
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if (head.status == 200) return "The file changed on the server";
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if (head.status != 206) return "The server answered " + std::to_string(head.status);
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if (head.chunked || head.rangeFrom != from) return "The server sent another part of the file";
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if (head.rangeTotal != total || head.rangeTo != total - 1 || head.contentLength != total - from) return "The file changed size on the server";
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if (!etag.empty() && !head.etag.empty() && head.etag != etag) return "The file changed on the server";
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return "";
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}
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// How long to keep trying. A break that came after new bytes is the link being poor, and is
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// worth another try; breaks with nothing in between mean it is not coming back.
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class ResumePolicy {
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public:
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static constexpr int kMaxResumes = 20; // in one download
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static constexpr int kMaxStuck = 3; // in a row without a byte
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// The connection broke with `received` bytes of the file here: try again?
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bool again(long received) {
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stuck_ = received > last_ ? 0 : stuck_ + 1;
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last_ = received;
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if (resumes_ >= kMaxResumes || stuck_ >= kMaxStuck) return false;
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resumes_++;
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return true;
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}
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int resumes() const { return resumes_; }
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private:
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long last_ = 0;
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int resumes_ = 0, stuck_ = 0;
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};
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} // namespace roro::release
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